Making Sense of Resource Block Grid in 5G NR.
Cellular data is carried over frequency resources (Subcarriers or SCs) transmitted over time-domain symbols. The combination of subcarrier and symbols is what makes the basis of the Resouce Grid (See Fig. 1).
In 5G NR Resource Grid, we have several terminologies that are often quite confusing for beginners so I’ll try to make them simple in this article.
Let's take it step by step.
1 The process of assigning data transmission resources is called Scheduling. The smallest unit of Scheduling Block that a gNB assigns for transmission comprises two adjacent Physical Resource Blocks (PRBs). These two adjacent PRBs make up one Slot. Hence the length of the slot is the minimum Transmission Time Interval (TTI). A slot length depends on the Sub-Carrier Spacing (SCS) also referred to as numerology. For example, SCS = 0 has a slot length is 1 ms, and SCS=1 has a slot length is 0.5 ms.
2. A RB (RB) is defined as 12 consecutive SCs in the frequency domain in 5G NR. The gNB schedules 14-symbol RBs at any given scheduling time.
3. The basic building block of PRBs is the Resource Element (RE). We cannot break resources further than REs. Each RE comprises one subcarrier over one Symbol.
